Cavities and active regions

ABSTRACT

The present invention relates to a method and apparatus for providing and/or receiving audible sound. In particular, the invention relates to apparatus, such as a micro speaker, which includes an active region which comprises a particulate adsorbent material comprising i) microporous organic polymer (MOP) material, and/or ii) metal organic framework (MOF) material treated with a hydrophobic coating or a membrane. The particulate adsorbent material is either in the form of loose or semi-loose granules, or it is supported by or impregnated into a woven, knitted or non-woven felt material. The apparatus of the present invention is suitable for use in an electronic device, for example a mobile or portable electronic device, to provide improved audible sound.

The present invention relates to a method and apparatus for providingand/or receiving audible sound. In particular, but not exclusively, thepresent invention relates to apparatus, such as a micro speaker forproviding audible sound, suitable for use in an electronic device, forexample a mobile or portable electronic device.

Portable consumer electronics devices, such as earphones, headphones,earbuds, tablets and mobile phones or other such mobile electronicdevices have continued to become more and more compact. As systemenclosures/casings become smaller and the space available for speakerintegration is reduced, so the space available for a speaker back volumedecreases, and along with it, low frequency acoustic performance. Suchspeakers are examples of apparatus for providing audible sound.

In order to combat this performance limitation many forms of adsorbentmaterials have been developed that use adsorption/desorption effects toincrease the acoustic compliance of these increasingly tiny cavities,thereby improving low frequency response. These materials have typicallyconsisted of zeolites and various forms of Activated Carbon (AC) and/orcarbon nanohorns. These materials have key drawbacks associated withtheir use.

For example, Zeolite based materials tend to be naturally stronglyhydrophilic, meaning that their acoustic performance diminishessignificantly when they are exposed to moisture in the air. A number ofstrategies have been developed to overcome this, dividing principallyinto barrier methods and hydrophobic treatments of the adsorbentmaterials themselves. These techniques can be complex, require severalpost-processes and may have questionable durability.

Carbon-based materials have a separate problem in that they areelectrically conductive, and so may cause short circuits if the materialinterferes with electronic circuitry. These types of materials may alsomask or interfere with the radio frequency emissions of any device inwhich they are positioned. This problem is exacerbated by the fact thatmany micro speaker housings have the associated device's antenna printeddirectly onto their backs.

There thus exists a need for a non-conductive and naturally hydrophobicadsorbent material with high acoustic performance that can be deployedin a way that fully maximises the small back-volume form factor madeavailable to the acoustic engineer.

Metal Organic Framework (MOF) materials have been developed separatelyprimarily for filtration and gas storage applications. These materialsare natural electrical insulators and have micropore geometries that canbe tuned to suit the need of the application, featuring surface areasthat vastly exceed those of conventional adsorbent materials such asactivated carbons.

Traditionally these materials have been fragile, expensive and unstable,though some are now emerging that are viable at industrial scales, suchas Aluminium Fumarate based MOFs. However, for adsorption/desorption totake place at frequencies up to 1000 Hz, as is needed in micro speakerapplications, the grain size of the material must be very small. Thiscauses three problems.

Firstly, a small grain size accentuates the materials potential forabsorbing moisture, as occurs with most Zeolite and other highlymicroporous materials. Secondly, small grain size causes the material topack into a very dense layer which can result in the material's flowresistivity becoming too high. This causes the micropores to becomeinaccessible to the acoustic field. In other words, as the materialpacks down into a densified bed it stops working, acoustically. Thirdly,use of small grain material gives rise to the increased possibility ofthe powder being lost to the system and finding its way intoneighbouring components or the outside air. Furthermore, according tocertain prior art techniques binding the material into a solid blockwill cause at least some of the micropores to be masked, with aresultant loss of performance.

It is an aim of the present invention to at least partly mitigate one ormore of the above-mentioned problems.

It is an aim of certain embodiments of the present invention to provideapparatus for providing and/or receiving audible sound, for example amicro speaker, suitable for use with a mobile electronic device (theterm “mobile electronic device” as used herein includes a mobile phone,a smart phone, a laptop, a tablet or personal assistant, an electronicdevice for displaying images such as a television, a monitor, an audiovisual projector or the like, a speaker such as a portable speaker, asmart speaker or a Bluetooth speaker, a vehicular speaker, a wearableelectronic device such as a watch, hearing aid, a wearable computer, anearphone, a wearable smart device, a wearable navigation aid and aheadphone), which apparatus includes one or more speakers and/ormicrophones that have superior acoustic performance relative toconventional techniques.

It is an aim of certain embodiments of the present invention to providea micro speaker or a micro speaker housing, that is to say a small-scalespeaker, that includes one or more active regions that compriseadsorbent material which may be optionally supported by a supportelement.

It is an aim of certain embodiments of the present invention to providea method of manufacturing a material that can be used in the manufactureof a speaker or microphone, and which results in a finished speaker ormicrophone having good performance in use.

It is an aim of certain embodiments of the present invention to providea material that can be incorporated in a way to enhance acousticperformance.

According to a first aspect of the present invention there is providedapparatus for providing and/or receiving audible sound, comprising:

-   -   a housing that provides at least one cavity region;    -   a vibratable element in or proximate to the cavity region; and    -   an active region;    -   wherein the active region comprises particulate adsorbent        material comprising i) microporous organic polymer (MOP)        material, and/or ii) metal organic framework (MOF) material        treated with a hydrophobic coating or a membrane.

Aptly the microporous organic polymer (MOP) material isPoly-dichloroxylene (P-DCX).

Aptly the metal organic framework (MOF) material comprises a structurein which metal ions act as nodes or joints to which organic ligands(linkers or struts) are attached and which can extend to other ligandmolecules. A suitable example is aluminium fumarate. The MOF is treatedwith a hydrophobic coating, or a membrane which may comprise theflexible membrane or the membrane material described below.

Aptly the adsorbent material further comprises one or more secondaryadsorbent materials. Aptly, the adsorbent material comprises less than50% by weight, of a secondary adsorbent material. Aptly the adsorbentmaterial comprises less than 15% by weight of a secondary adsorbentmaterial.

Aptly the secondary adsorbent material comprises one or more materialsselected from activated charcoal and zeolite.

Aptly the adsorbent material is porous and has pores in the region of 1nm to 10 nm in diameter.

Aptly the pores each have an average diameter of about around 2 nm.

Aptly the adsorbent material is microporous.

Aptly the adsorbent material is mesoporous.

Aptly the adsorbent material will be of mixed porosity.

Aptly the adsorbent material is a gas-adsorbing material.

Aptly the adsorbent material is in the form of separate particles, forexample as granules or powder.

Aptly at least 80% by weight, preferably at least 95% by weight, of theadsorbent material particles have a maximum diameter of 120 microns,preferably a maximum diameter of 100 microns, further preferably amaximum diameter of 85 microns. Particularly favourable results areobtained when the adsorbent material passes through a 1/10 to 1/12 mmmesh.

Aptly the adsorbent material provides a surface area of at least 500m²/g.

Aptly the adsorbent material has a cage-like structure.

Aptly the adsorbent material is a material is non-crystalline.

Aptly, the adsorbent material does not have an ordered structure, andoptionally it comprises an amorphous microstructure.

Aptly the adsorbent material is not electrically conductive.

Aptly the adsorbent material is an insulating material.

Aptly the adsorbent material is naturally hydrophobic.

Aptly the adsorbent material is used in loose (including semi-loose)particulate form.

Aptly the adsorbent material is treated to allow a stabilised crust orskin to form.

Aptly the adsorbent material is treated by saturating with a solventwhich slightly solubilises the top surface of the adsorbent material.Methanol has been found to work well, however, other relatively lowboiling point solvents are also useful.

Aptly the adsorbent material is retained in position within theapparatus of the present invention by a support element.

Aptly the adsorbent material is held within the active region by thesupport element.

Aptly the adsorbent material is supported by the support element.

Aptly the adsorbent material is coated on an outer surface of thesupport element.

Aptly the adsorbent material is embedded throughout a supportingmaterial that provides the support element.

Aptly the adsorbent material is impregnated in the supporting materialthat provides the support element.

Aptly the support element comprises a woven structure provided byinterwoven threads of the support material.

Aptly the support element comprises a knitted structure provided byinterlocking looped threads of the support material.

Aptly the support element comprises a non-woven felt.

Aptly the felt is provided by randomly orientated or pseudo randomlyorientated strands of the support material.

Aptly the adsorbent material is impregnated in the support element witha fill factor of at least 60%.

Aptly the fill factor is at least 80%.

Aptly the support element comprises woven, knitted or non-woven threadsor strands which are generally disposed in a spaced apart relationshipand which define a plurality of spaces.

The adsorbent material is carried on the threads or strands and/or iscontained within these spaces.

Aptly the support element (preferably in the case where the supportelement is a non-woven material, for example felt) is sealed with one ormore sheets of a sealing material. Aptly the support element (preferablyfelt) is sealed between a first and a further sheet of a sealingmaterial.

Aptly the support element is sealed via a thermal process.

Aptly the sealing material is a flexible membrane.

Aptly the flexible membrane is moisture impermeable.

Aptly the flexible membrane has a thickness of less than 0.5 mm.

Aptly the flexible material is a fine poro-elastic gauze material.

Aptly the flexible membrane comprises silk.

Aptly the support element comprises a porous container suitable forcontaining the adsorbent material.

Aptly the porous container is constructed from a membrane material.

Aptly the membrane material is moisture impermeable.

Aptly the membrane material has a thickness of less than 0.5 mm.

Aptly the membrane material is a fine poro-elastic gauze material.

Aptly the membrane material comprises silk.

Aptly the active region comprises a region of the housing of theapparatus of the present invention.

Aptly the active region comprises at least one wall member of thehousing.

Aptly the active region comprises walls of the housing that are providedas the active region.

Aptly the active region comprises a panel or panels or body or bodiescontained within the cavity region.

Aptly the active region comprises a flexible bag including adsorbentmaterial in the cavity region or the active region comprises at leastone wall member of the housing and a panel or panels in the cavityregion or the active region comprises at least one wall member of thehousing and at least one flexible bag including adsorbent material inthe cavity region.

Aptly the flexible bag is constructed from a membrane material.

Aptly the membrane material is moisture impermeable.

Aptly the membrane material has a thickness of less than 0.5 mm.

Aptly the membrane material comprises silk material.

Aptly there is provided a speaker or microphone that comprises theapparatus according to the first aspect of the present invention.

Aptly the active region is in fluid communication with at least a rearsurface of the vibratable element and/or optionally is in fluidcommunication with the cavity region.

According to a second aspect of the present invention there is provideda mobile electronic device as described above, comprising:

-   -   a case body; and    -   at least one speaker unit or microphone unit in the case body;        wherein    -   each speaker unit or microphone unit comprises a housing that        defines at least one cavity region, a vibratable element in or        proximate to the cavity region and an active region that        comprises adsorbent material comprising microporous organic        polymer (MOP) material, and/or a metal organic framework (MOF)        material treated with a hydrophobic coating or a membrane.

Aptly the at least one speaker unit comprises a main external speakerunit of the mobile electronic device and/or an ear speaker unit of themobile electronic device.

Aptly the mobile electronic device comprises a mobile phone.

Aptly the mobile phone comprises a smart phone.

Aptly the mobile electronic device comprises an earphone or tablet orlaptop or digital assistant or watch or smart wearable or navigation aidor headphone or TV or monitor or portable speaker or smart speaker orBluetooth speaker or vehicular speaker.

Aptly the mobile electronic device is wearable.

Aptly the mobile electronic device further comprises a speaker driver ineach speaker unit; and a controller for providing drive signals to thespeaker driver.

Aptly each speaker driver comprises a voice coil or at least one MEMSdevice and at least one diaphragm element.

Aptly the mobile electronic device comprises a display.

Aptly the display is a touchscreen.

According to a third aspect of the present invention there is provided avolume-enhancing material for use in a micro speaker or loudspeakerconfiguration, wherein the adsorbent material comprises a Metal OrganicFramework (MOF) material treated with a hydrophobic coating or membrane,and/or an amorphous microporous organic polymer (MOP), featuringcomponent materials with innate hydrophobicity, such asPoly-dichloroxylene (P-DCX).

According to a fourth aspect of the present invention there is provideda speaker system, comprising:

-   -   a speaker unit; and    -   a cabinet forming a chamber at a back region or side region of        the speaker unit largely filled with particulate        volume-enhancing adsorbent material comprising a metal organic        framework material treated with a hydrophobic coating or a        membrane, and/or an amorphous microporous organic polymer (MOP)        such as Poly-dichloroxylene (P-DCX), wherein optionally the        adsorbent material is supported by a support element, and        further wherein optionally the particles of the volume-enhancing        adsorbent material are treated to cause a stabilised crust to        form, for example by saturating the particles of the volume        enhancing adsorbent material with methanol, before being covered        with a flexible membrane, preferably comprising a fine        poro-elastic gauze material, or silk.

According to a fifth aspect of the present invention there is provided aspeaker system, comprising:

-   -   a speaker unit; and    -   a cabinet forming a chamber at a back region or side region of        the speaker unit largely filled with a felt support element        comprising of a gas permeable upper layer, particles of an        adsorbent material dispersed at high concentrations within a        fibrous matrix without using binder, and a permeable or        impermeable back layer; wherein    -   the adsorbent material comprises a metal organic framework        material treated with a hydrophobic coating, and/or an amorphous        microporous organic polymer (MOP) material, featuring component        materials with innate hydrophobicity, such as        Poly-dichloroxylene (P-DCX).

According to a sixth aspect of the present invention there is provided amicrophone system, comprising:

-   -   at least one transducer element for converting sound to an        electrical signal;    -   optionally a preamplifier that receives an output from the        transducer element;    -   a housing or cabinet at a back region or side region of the        transducer element; and    -   an active region that comprises adsorbent material comprising        microporous organic polymer (MOP) material, and/or metal organic        framework (MOF) material treated with a hydrophobic coating or a        membrane.

Aptly the transducer element converts air pressure variations associatedwith sound waves to an electrical signal.

Aptly the microphone system is a dynamic microphone or a condensermicrophone or a piezoelectric microphone.

Aptly there is provided a mobile electronic device that comprises themicrophone system according to the sixth aspect of the presentinvention.

Aptly the mobile electronic device is a mobile phone or hearing aid.

Certain embodiments of the present invention provide apparatus forproviding and/or receiving audible sound in which an active region thatcomprises an adsorbent material as described above and which enhancesacoustic performance relative to conventional techniques.

Certain embodiments of the present invention utilise a microporousorganic polymer (MOP) material and/or a metal organic framework (MOF)material supported on or in a support element that can be a felt or awoven, knitted or a non-woven material body.

Certain embodiments of the present invention provide a method ofmanufacturing a microphone and/or a speaker such as a micro speaker orloudspeaker.

Certain embodiments of the present invention provide metal organicframework-based material and/or microporous organic polymer-basedmaterial which achieves performance benefits for a loudspeaker ormicrophone relative to conventional techniques in a cost effective,highly stable and hydrophobic form. This can be achieved by usingparticulate metal organic framework material and/or particulatemicroporous organic polymer material, either as loose material, or in acoating or an impregnate for a support element.

Certain embodiments of the present invention provide microporous organicpolymer-based materials which are synthesised from component parts whichare innately hydrophobic, which results in a material with a high degreeof natural hydrophobicity.

Certain embodiments of the present invention provide a speaker and/ormicrophone and/or cabinet for a speaker and/or microphone in whichmaterials are presented to a sound field in an uncompacted andbinderless aerated suspension. This can be achieved by impregnating afine non-woven felt structure using ultrasonic or electrostaticentrainment methods. Such ultrasonic/electrostatic methods may achievefill factors of 80%.

Certain embodiments of the present invention will now be describedhereinafter, by way of example only, with reference to the accompanyingdrawings in which:

FIG. 1 illustrates an exploded view of an ear speaker;

FIG. 2 illustrates a cross section through the ear speaker;

FIG. 3 illustrates an exploded view of an alternative speaker;

FIG. 4 illustrates an alternative speaker with side chambers filled withactive region but with a remaining central region empty;

FIG. 5 illustrates a cross section through a speaker;

FIG. 6 illustrates a cross section through a speaker;

FIG. 7 illustrates low frequency response of empty and selectedpartially filled micro speakers according to the present invention;

FIG. 8 illustrates higher range frequency response of empty and selectedpartially filled micro speakers according to the present invention;

FIG. 9 illustrates differential frequency response (SR filled-SR empty)of selected partially filled micro speakers according to the presentinvention;

FIG. 10 illustrates electric impedance of micro speakers according tothe present invention with an empty case and selected fillings;

FIG. 11 illustrates particle size effects;

FIGS. 12a to 12f illustrate frequency response with different fillings;

FIG. 13 illustrates electric impedance response; and

FIG. 14 illustrates differential frequency response.

In the drawings like reference numerals refer to like parts.

Certain embodiments of the present invention relate to a mobileelectronic device and to apparatus in a mobile electronic device forgenerating audible sound. As mentioned above, a mobile electronic devicecan be a mobile phone such as a smartphone or laptop or earphone orearbud or headphones or navigation device or TV or monitor or smartspeaker or Bluetooth speaker or vehicular speaker, or can be a wearableelectronic device such as a smartwatch or smart clothing. The apparatusfor providing audible sound can be a speaker or the like. The speakercan be small in which situation the speaker may be referred to as a minispeaker or micro speaker. An example of a micro speaker is an earspeaker or main external speaker of a smartphone.

A typical smartphone (for example a Samsung Galaxy S8 smartphone)includes a rear casing that has a grill for an ear speaker. Inoperation, the ear speaker generates sound pressure waves which providesound audible to a human ear when it exits from an internal regionwithin the housing where an ear speaker is located via multiple throughapertures in the grill to the listener. In addition to the ear speaker,a smart phone may also include one or more further speaker units andgenerally one of these further speaker units is designated a mainexternal speaker designed to provide audible sound through an exitaperture in a side panel of the smartphone. The side panel can be partof the overall smart phone casing, which forms a housing for thesmartphone and supports a touchscreen.

FIG. 1 illustrates an exploded view of the ear speaker. A speaker 200includes a cabinet housing 410 which encompasses a “back-volume” whichcan be occupied (partially or fully) by a volume-enhancing activeregion. In the embodiment illustrated in FIG. 1 the cabinet housing 410encompasses a back volume which is occupied by a volume enhancingmaterial 420 which comprises adsorbent material comprising microporousorganic polymer material and/or metal organic framework material whichmay optionally be treated with a hydrophobic coating. The volumeenhancing material 420 comprises adsorbent material in the form ofgranules or powder which may be loose/semi-loose or in conjunction witha support element. As shown, the adsorbent material is covered by a thinmembrane 430 which helps prevent material escaping and which can helpprotect the active region from moisture ingress. The thin membrane islocated between the active region and an upward (in FIG. 1) facingloudspeaker driver 440 comprising a vibratable element 470 which is theelement which provides soundwaves audible as sound. Aptly the thicknessof the flexible membrane is less than 0.5 mm. The housing for thespeaker has a front plate 450 which helps complete the compositeenclosure. In an alternative embodiment, the ear speaker 200 illustratedin FIG. 1 may instead be a microphone unit for receiving sound. In thisembodiment, the loudspeaker driver 440 may be replaced with a soundreceiving unit such as a transducer element comprising a vibratableelement which is the element which receives soundwaves and converts theair pressure variations associated with the soundwaves into anelectrical signal. Optionally a preamplifier receives an output from thetransducer element. It will be appreciated that according to certainaspects of the present invention, the microphone unit may be provided inproximity to or in a different location to a speaker unit. For example,the smartphone casing may comprise a further aperture which may enableaudible sound to pass into the smartphone for reception by a microphoneunit. It will also be appreciated that according to certain embodimentsof the present invention one, two, three or more microphone units may beprovided in a mobile device. In a further embodiment, at least onespeaker unit and at least one microphone unit may be provided as acomposite unit.

FIG. 2 illustrates a cross section through the ear speaker shown in FIG.1 in more detail.

FIG. 3 illustrates an exploded view of an alternative speaker 600 whichcan, for example, be utilised as an external speaker. This includes ahorn-like acoustic neck 610 that includes a channel for sound to feedout through the exit aperture in a casing of a smartphone. As shown inFIG. 3 the speaker 600 includes a speaker housing 710 which sits in anouter cavity 715 provided by an outer housing 717 in which an activeregion of volume enhancing material 718 is provided. In the embodimentshown in FIG. 3 the active region is a generally C-shaped region. Aloudspeaker driver 740 which comprises a vibratable element 790 sitswithin the smaller internal speaker housing 710 and that smaller speakerhousing 710 is partially closed by a cover 750. An outer cavity definedby the main outer housing 717 is closed by a cover plate 760. Thespeaker thus includes an inward facing loudspeaker 710, 740, 750 thatsits within a larger volume defined by an outer housing 717, 760augmented by a volume enhancing material 718. The driver 740 facesdownwards (in FIG. 3) acting to generate pressure fluctuations withinthe cavity 770 within the inner housing 710. This horn like cavity 770feeds sound to the outside of the device via an acoustic channel 780.The outer cavity defined by the lower housing 717 and the plate or cover760 is acted upon by the rear of the driver. The volume enhancingmaterial of the active region within this cavity acts to increase theacoustic compliance of the air inside the cavity thereby improving lowfrequency response.

FIG. 4 illustrates a speaker similar to that shown in FIG. 3, but with acover plate 960 removed to reveal an active region with a basicrectangular design augmented with one or more (three shown) sidechambers 910, 920, 930. In the embodiment illustrated in FIG. 4, theside chambers are full of volume enhancing material (an active region),whereas the back volume (the cabinet housing 840) is clear of fillmaterial

In a similar but alternative embodiment of FIG. 4 (alternativeembodiment not shown), all of the side chambers and the main chamber arefilled with a volume-enhancing material (the active region).

FIG. 5 illustrates a cross section of a speaker featuring a horn likeinternal acoustic cavity similar to that shown in FIG. 4. FIG. 5 helpsillustrate how a side chamber 930 includes an active region that iscovered by a membrane 1025. The active region comprises adsorbentmaterial which comprises microporous organic polymer material and/ormetal framework material treated with a hydrophobic coating. Theadsorbent material is in particulate form either provided asloose/semi-loose granules, or in conjunction with a support element.FIG. 5 also helps to illustrate how the active region 930 can be influid communication with an outer region of the loudspeaker driver 740to thereby increase acoustic compliance of the air inside the cavity andthereby improve low frequency response.

FIG. 6 also illustrates a cross section through a speaker which includesa horn-like internal acoustic cavity and is similar to that shown inFIG. 5. In this embodiment, a back volume is augmented by volumeenhancing material, optionally provided by loose/semi-loose granules ofadsorbent material optionally covered by a membrane. Alternatively, thevolume enhancing material may be provided in combination with a supportelement, for example a felt material which is coated or impregnated withmicroporous organic polymer (MOP) material and/or metal organicframework (MOF) material treated with a hydrophobic coating or amembrane.

The cabinet forming the horn cavity is formed from a conventionalplastic wall. An acoustic enclosure around the back volume is formedfrom a high-density impermeable shell component 1110. The impermeableshell is bonded to the plastic walls of the horn component using glue(or binder or other such element) with a suitable overlapping tab toensure that the back-volume enclosure is acoustically sealed.

Certain embodiments of the present invention relate to a smartphonemicro speaker.

It has been determined that there is an acoustic benefit of providing anactive region on the low frequency response (sub 900 Hz) behaviour of amobile phone without causing electromagnetic masking of the behaviour ofthe phone antenna. Around a 3 dB improvement may be achieved. In oneembodiment, the active region can be incorporated into the back volumeof a micro speaker enclosure, either in loose/semi-loose form or inconjunction with a support element.

According to certain embodiments of the present invention an averagegain of 3.49 dB is achieved with a silk-mesh-supported insertion ofloose/semi-loose powder into an empty micro speaker.

Electric impedance and near-field frequency response of a micro speakercan be measured within a Bruel and Kjaer soundproof BOX, mounted withina structure that allows position fixing and a microphone distance of 10mm from the speaker outcome. Audiomatica SRL—CLIO equipment andsoftware, release 1.4, pocket version was used to perform themeasurements.

The equipment consists of a CP-01 audio interface box and a condenserelectret microphone (with accuracy of 1 dB from 20 Hz to 10 kHz). Theaudio interface with analog RCA connections and sampling frequencies of96 and 48 kHz, containing:

-   -   A signal generator of 1 Hz-45 kHz, with a frequency accuracy of        0.01% and resolution of 0.01 Hz.    -   An AC analyser of 24 bit sigma delta A/D converter and an input        range of +40 dBV down to −40 dBV    -   A DC analyser of 12 bit A/D Converter with an input range of        +6.5V to −6.5V

The performance enhancement of a micro speaker was measured afterfilling approximately 85-90% of its cavity with adsorbent material inthe form of loose/semi-loose MOP powder sealed with a silk fabric. Otherfill factors can of course be utilised. Empty and partially filled microspeakers were measured by these means, obtaining the electric impedanceand frequency response. The improvement in performance was calculatedafterwards as the difference between the frequency response of thepartially filled and the empty micro speaker. In order to take accountfor the errors associated with the position of the microphone andspeaker, several measurements were taken, and a correlation wasestablished through standard deviation. As a non-limiting example, theMOP material may be polymerised dichloroxylene (P-DCX).

Test Results

A total of 28 micro speakers have been tested with an active region.

After the selection of an adequate glue and filling procedure(appropriate sealing mesh), 11 micro speakers were successfully enhancedbut at different rates.

TABLE 1 Example filling characteristics for micro speakers Type of(partial, Speaker Trace notation 85-90%) Mean ΔfR [dB] Name in FIG. 7-10filling f₀ [Hz] 100 Hz < f < 900 Hz Empty

Empty closed 897.6 ≈ micro speaker V₀ speaker Speaker B

Loose MOP powder 760.5 ≈ 3.4966 contained behind a 1.18 V₀ silk fabric.Speaker D

Methanol-hardened 804.7 ≈ 2.8749 loose MOP powder 1.12 V₀ contained witha silk fabric.

Table 1 presents the filling characteristics of the micro speakers thatpresented best frequency response enhancement and a summary of theirperformance. The selection included two micro speakers partially filledwith loose microporous organic polymer (MOP) material, as it wasperceived that an extra step was needed in order to retain the powderwithin the speaker when it was functioning inside the phone. For thispurpose, a micro speaker was filled with wet MOP that produced ahardened surface, stopping it from leaking outside the speaker duringoperation, causing a slight performance penalty.

FIGS. 7 to 10 show low frequency response, wider range frequencyresponse, differential frequency response and electric impedance(resonant frequency) of an empty micro speaker (shown as ‘-’ in FIGS.7-10), a micro speaker sample with loose MOP (silk protected) inclusion(speaker B, shown as ‘- - -’ in FIGS. 7-10), and a micro speaker samplewith hardened loose MOP (silk protected) inclusion (speaker D, shown as‘-. - . -.’ in FIGS. 7-10).

The highest performance was obtained by speaker B, with a mean gain ofapproximately 3.5 dB and a shift in the resonant frequency of about 140Hz, establishing that the cavity is behaving as if it was ˜18% larger.Speaker D, with a hardened MOP skin achieved a main gain of about 3 dBwith slightly less resonant frequency shifting, increasing the volume by˜12%.

FIG. 7 shows that in the very low frequency end, loose filled microspeakers produced a significant enhancement.

FIG. 8 shows the frequency response of the selected partially filledmicro speakers for a broader frequency range, reaching to 6000 Hz. Itcan be seen that loose MOP filled micro speakers cause a shift in thepeak performance by about 250 Hz to the right, reaching maximumperformance at a frequency of about 4000 Hz.

FIG. 9 shows the relative frequency response of the various filledspeakers to the empty case across the lower frequency range. Theimprovement in the very low frequency range is much higher with theloose MOP filled micro speakers.

FIG. 10 shows the electric impedance of the filled micro speakerscompared to the empty micro speaker. The biggest compliance enhancementis seen by the inclusion of loose MOP in Speaker B; the peak shifted byabout 140 Hz corresponding to an increase of ˜18% of the initial cavityvolume. It can be seen that the inclusion of the Methanol-hardened MOPin Speaker D, exhibits a more damped resonant response (the peak shiftedby about 100 Hz, equating to an apparent increase of volume of ˜11.5%),which leads to the conclusion that this preparation method may not beallowing the MOP to reach its potential enhancement performance.

Notably, a mean differential frequency response below 900 Hz of about 3dB has been achieved for a micro speaker by introducing MOP as a drypowder within a silk mesh, filling about 85-90% of the micro speakercavity.

This encapsulation method was found to present a limited risk ofmaterial leaking from the speaker, so an additional method has beentested and found to achieve close to 3 dB gains:

-   -   Saturating the powder with methanol (pre-treated) to leave a        crust, then covered with the silk mesh

While loose MOP powder achieves the best performance, the pre-treatedloose MOP loudspeaker achieves the highest improvement in the very lowfrequency end.

It has been found that reducing the grain size of materials has asignificant effect on their performance within the target range, withPoIMOF materials (P-DCX) that had previously shown poor performancebeing transformed into lead candidates (see FIG. 11). Notably, siftedPoIMOF material (is sifted P-DCX, herein referred to as ‘PoIMOFg2’)which passes through a mesh in the range 1/10- 1/12 mm showsimprovements in frequency response of about around 3-5 dB in the 400-700Hz frequency range in 1 cm deep loudspeaker cavities with 75% materialfill. The MOP materials out-performed zeolite, perlite and silicareference materials, and produced very similar performance tohigh-activation carbon powders.

For materials in a representative speaker box, of about 58 mL volume, ithas been found that a 60%-80% filling of MOF and/or MOP materials mayintroduce a benefit of ˜1.5 dB at the low frequency spectrum, whilereducing the performance around the resonant frequency of the speakerand above. Although the low frequency response of micro speakers with aMOP material (e.g. P-DCX) which may be referred to as ‘PoIMOF’ and/or aMOF material (e.g. an Aluminium Fumerate based MOF) which may bereferred to as ‘NewMOF’ herein treated with a hydrophobic coating or amembrane, is slightly down on the results obtained for activated carbonpowder, MOP/MOF materials nevertheless provide significant furtherbenefits such as introducing less damping and therefore betterperformance is achieved by their inclusion. Performance is illustratedin FIGS. 12a to 12f , with the most favourable results being illustratedin FIGS. 12e and 12f for the PolMOFg2 material.

The following presents results obtained for 12 MOP-partially filledmicro speakers, in loose powder form attached by a silk mesh.

Table 2 below presents filling characteristics and main measuredobtained parameters for each partially filled micro speaker.

FIGS. 13 and 14 display impedance shifting (resonant frequency) of theenhanced micro speakers and the differential frequency response for eachcase. It should be noted, that while Speaker P showed high enhancement,it was outperformed by speaker B, with similar filling procedures.

Complete Improved Micro Speaker List

TABLE 2 Complete list of filling characteristics for micro speakers Typeof Speaker Trace notation (partial, 85- Mean ΔfR [dB] Name in FIG. 13,14 90%) filling f₀ [Hz] 100 Hz < f < 900 Hz Empty micro

Empty closed 897.6 ≈ — speaker speaker V₀ spkB

Loose MOP/silk 760.5 ≈ 3.4966 fabric. 1.18 V₀ spkD

Methanol- 804.7 ≈ 2.8749 hardened MOP/ 1.12 V₀ silk fabric. spkP

Loose MOP/silk 786.8 ≈ 2.825 fabric. 1.14 V₀ spkX Not shown LooseMOP/silk 810.8 ≈ 2.0605 fabric. 1.11 V₀ spkN Not shown Loose MOP/silk801.7 ≈ 1.8227 fabric. 1.12 V₀

The procedure for filling the micro speakers involved un-gluing thejunctions of the speakers with heat and a scalpel. Once the device wasopen and divided into two parts, the material filling was introduced.

-   -   Speaker B: about 80% of the volume of the speaker was filled        with loose MOP and two silk pieces cut in the shape of the        back-cavity parts were glued in the internal boundary of the        back cavity, protecting the loose MOP from leaving the area. The        back and front original parts of the speakers were then glued        back with liquid fast operating glue and clamped during the        curing process of the glue to create an air-tight seal.    -   Speaker D: Methanol was poured into the MOP, in order to wet it        until achieving a consistency that is loose enough to allow        easier pouring in the back cavity of the speaker. The wet        process allowed to pour more MOP than when it was dried filling        about 80% of the volume. Again, the two silk pieces (cut in the        shape of the back-cavity parts) were glued in the internal        boundary of the back cavity. The back and front original parts        of the speakers were then glued back with liquid fast operating        glue and clamped during the curing process of the glue to create        an airtight seal. The glued speaker was left at a temperature of        around 70° C. for around 12 hours to evaporate the methanol from        the MOP.

Metal-organic framework (MOF) materials are hybrid materials that takeadvantage of the properties of both organic and inorganic porousmaterials, and they form stable, ordered and high surface areasstructures.

Metal organic framework (MOF) materials are known as porous coordinationnetworks, porous coordination polymers (PCPs) etc.

Certain metal organic framework (MOF) materials possess one or more ofthe following characteristics:

-   -   1. multifunctional hybrid (inorganic-organic) materials    -   2. formed of metal ions (nodes or joint) to which organic        ligands (linker or strut) attach and extend to other ligand        molecules—components provide endless possibilities    -   3. 3D crystalline structure (although can also be 1D or 2D)5.    -   4. Have an “indefinite” extent    -   5. Nanoporous—have large pore sizes and ultrahigh porosity (up        to 90% free volume)    -   6. Extremely large internal surface area typically» 1,000 m2/g        (extending beyond 6,000 m2/g)    -   7. Selectively uptake small molecules    -   8. Can have optical or magnetic responses to the inclusion of        guests    -   9. Synthesis from molecular building blocks holds the potential        to tailor the properties of the resulting MOF    -   11. Behave akin to molecular sponges    -   12. Functionalist ion of the organic unit can provide        predictably functionalised pores

Typically, MOFs are synthesised by combining organic ligands and metalsalts in solvothermal reactions at relatively low temperatures (below300 degrees Celsius).

Characteristics/structure of the resulting MOF is influenced by:

-   -   1. Characteristics of the ligand (bond angles, ligand length,        bulkiness chirality etc.)    -   2. Metal ion used: tendency to adopt certain geometries

Reactants mixed in high boiling polar solvents e.g. water, dialkylformamides, dimethyl sulfoxide or acetonitrile or the like.

Concentrations of both metal salt and organic ligand which can be variedacross a large range, extent of solubility of reactants, pH of thesolution.

There are also several other methods for treatment e.g. electrochemical,microwave irradiation et al.

Secondary building units (SBUs) dictate the final topology of theframework. Organic linkers seldom change structure during assembly. TheSBUs are often metal clusters based and result from the initial bondingbetween the metal ions and bridging ligands. Can form several shapese.g. trigonal planar, square planar tetrahedral. Shape of SBU depends onstructure of ligand, type of metal, ratio of metal to ligand, solvent,and source of anions to balance metal ion charge.

Pores are the void spaces formed within MOFs upon the removal of guestmolecules.

In general, large pores are advantageous for conducting host-guestchemistry such as catalysis therefore mesoporous (openings between 20and 500 Å) or macroporous (greater than 500 Å) materials are attractive.

Microporous (less than 20 Å) materials have smaller pores which resultin strong interactions between gas molecules and the pore walls makingthem good for gas storage or gas separation applications.

Measurements of openings is performed from atom to atom whilesubtracting the van der Waals radii to give the space available foraccess by guest molecules.

Pores are usually occupied by solvent molecules that must be removed formost applications. Structural collapse can occur, the larger the porethe more likely this is. Permanent porosity results when frameworkremains intact.

Frameworks can interpenetrate one another to maximize packingefficiency.

MOFs may participate in post-synthetic modification (PSM) where furtherchemical reactions can be used to decorate the frameworks. This may beapplied to modify the surface property and pore geometry.

A range of MOF and amorphous microporous organic polymer (MOP) materialscan be utilised to provide an active region according to certainembodiments of the present invention. They can achieve performancebenefits of traditional loudspeaker-enhancing materials, but in acost-effective, highly stable and hydrophobic form by virtue of thesupport material they may be impregnated within. In the case of MOPmaterials, the microporous impregnate material itself is highlyhydrophobic which has benefits.

The MOP materials can be synthesized from component parts with innatehydrophobicity, resulting in a high degree of natural hydrophobicity ifthe resultant material. The material is preferably presented to thesound field in an uncompacted and binderless aerated suspension.

This can be achieved by impregnating the microporous organic polymer(MOP) material into a fine non-woven felt structure using ultrasonic orelectrostatic entrainment. Preferably a fill factor of 80% is achieved.

The felt can then be thermally sealed to keep the powder in using a thinand flexible impermeable membrane, which further adds to the materialsimmunity to the effects of moisture. This encapsulated felt with highadsorbent material content can be held close to the loudspeaker elementwithin the housing.

FIG. 7 illustrates a frequency response curve for a micro speaker (forexample as per the speaker shown in FIG. 4).

The solid black line (A) represents the acoustic frequency response ofan empty micro speaker, with no filling material.

The dashed line (B) shows the frequency response of the micro speakerwhen the side chambers are around 80% occupied by loose, dry MOP powdercovered by a silk membrane. The improvement over the empty case isaround 3.5 dB under 900 Hz.

The chain dashed line (C) shows the response curve of the micro speakerfor the same volume of MOP powder, this time fixed through saturation byMethanol which is evaporated prior to being covered by the silkmembrane. The improvement over the empty case is 2.87 dB below 900 Hz,but the shape of the curve is different, with more improvement now seenat very low frequencies (under 200 Hz), and with the resonant peak at800-1000 Hz damped down by around 4 dB. The combination of these effectsresults in a broader, more refined (if slightly quieter) sound quality.

This range of outcomes represents an opportunity to tune the beneficialresponse according to the desire of the customer.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of them mean “including but notlimited to” and they are not intended to (and do not) exclude othermoieties, additives, components, integers or steps. Throughout thedescription and claims of this specification, the singular encompassesthe plural unless the context otherwise requires. In particular, wherethe indefinite article is used, the specification is to be understood ascontemplating plurality as well as singularity, unless the contextrequires otherwise.

Features, integers, characteristics or groups described in conjunctionwith a particular aspect, embodiment or example of the invention are tobe understood to be applicable to any other aspect, embodiment orexample described herein unless incompatible therewith. All of thefeatures disclosed in this specification (including any accompanyingclaims, abstract and drawings), and/or all of the steps of any method orprocess so disclosed, may be combined in any combination, exceptcombinations where at least some of the features and/or steps aremutually exclusive. The invention is not restricted to any details ofany foregoing embodiments. The invention extends to any novel one, ornovel combination, of the features disclosed in this specification(including any accompanying claims, abstract and drawings), or to anynovel one, or any novel combination, of the steps of any method orprocess so disclosed.

The reader's attention is directed to all papers and documents which arefiled concurrently with or previous to this specification in connectionwith this application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

1. Apparatus for providing and/or receiving audible sound, comprising: ahousing that provides at least one cavity region; a vibratable elementin or proximate to the cavity region; and an active region thatcomprises a particulate adsorbent material comprising i) microporousorganic polymer (MOP) material, and/or ii) metal organic framework (MOF)material treated with a hydrophobic coating or a membrane.
 2. Theapparatus according to claim 1 wherein the adsorbent material is porousand has pores in the region of 1 nm to 10 nm in diameter.
 3. Theapparatus according to claim 1 or 2 wherein the adsorbent material ismicroporous.
 4. The apparatus according to any of claims 1 to 3 whereinthe adsorbent material has a cage-like structure.
 5. The apparatusaccording to any of claims 1 to 4 wherein the adsorbent materialprovides a surface area of at least 500 m²/g.
 6. The apparatus accordingto any of claims 1 to 5 wherein the adsorbent material is a materialthat does not have an ordered structure.
 7. The apparatus according toany of claims 1 to 6 wherein at least 80% by weight of the adsorbentmaterial particles have a maximum diameter of 120 microns.
 8. Theapparatus according to claim 1 wherein microporous organic polymer (MOP)material comprises poly-dichloroxylene (P-DCX).
 9. The apparatusaccording to claim 1 wherein the metal organic framework (MOF) materialis aluminium fumarate.
 10. The apparatus according to any of claims 1 to9 wherein the adsorbent material comprises one or more secondaryadsorbent materials.
 11. The apparatus according to any preceding claimwherein the adsorbent material is in loose/semi-loose particulate form.12. The apparatus according to claim 11 wherein the adsorbent materialis retained in position within the apparatus by a support element. 13.The apparatus according to any of claims 1-10 and 12 wherein theadsorbent material is coated on an outer surface of the support element.14. The apparatus according to any of claims 1-10 and 12 wherein theadsorbent material is embedded throughout a supporting material thatprovides the support element.
 15. The apparatus as claimed in claim 12wherein the adsorbent material is impregnated in a supporting materialthat provides the support element.
 16. The apparatus as claimed in claim15 wherein the adsorbent material is impregnated in the support elementwith a fill factor of at least 60%.
 17. The apparatus as claimed inclaim 12 wherein the support element comprises a woven structureprovided by interwoven threads of a support material, or a knittedstructure provided by interlocking looped threads of a support material,or a non-woven structure provided by randomly oriented or pseudorandomly orientated strands of support material.
 18. The apparatusaccording to claim 12 wherein the support element is sealed between oneor more sheets of a sealing material.
 19. The apparatus according toclaim 18 wherein the sealing material is a flexible membrane.
 20. Theapparatus according to claim 19 wherein the flexible membrane ismoisture impermeable.
 21. The apparatus according to claim 12 whereinthe support element is sealed via a thermal process.
 22. The apparatusas claimed in claim 1 wherein the active region comprises a flexible bagincluding adsorbent material in the cavity region or the active regioncomprises at least one wall member of the housing and a panel or panelsin the cavity region or the active region comprises at least one wallmember of the housing and at least one flexible bag including adsorbentmaterial in the cavity region.
 23. A speaker or microphone comprisingthe apparatus according to any preceding claim.
 24. A mobile electronicdevice, comprising: a case body; and at least one speaker unit ormicrophone unit in the case body; wherein each speaker unit ormicrophone unit comprises a housing that defines at least one cavityregion, a vibratable element in or proximate to the cavity region and anactive region that comprises a particulate adsorbent material comprisingi) microporous organic polymer (MOP) material, and/or ii) metal organicframework (MOF) material treated with a hydrophobic coating or amembrane.
 25. The mobile electronic device according to claim 24selected from a mobile phone, a smart phone, a laptop, a tablet orpersonal assistant, an electronic device for displaying images such as atelevision, a monitor, an audio visual projector or the like, a speakersuch as a portable speaker, a smart speaker or a Bluetooth speaker, avehicular speaker, a wearable electronic device such as a watch, hearingaid, a wearable computer, an earphone, a wearable smart device, awearable navigation aid and a headphone.
 26. A volume-enhancing materialfor use in a micro speaker or loudspeaker configuration, wherein thevolume-enhancing material comprises particulate adsorbent materialcomprising i) microporous organic polymer (MOP) material, and/or ii)metal organic framework (MOF) material treated with a hydrophobiccoating or membrane.
 27. A speaker system, comprising: a speaker unit;and a cabinet forming a chamber at a back region or side region of thespeaker unit largely filled with a volume-enhancing fine particle MetalOrganic Framework material, or an amorphous microporous organic polymer(MOP) such as Poly-dichloroxylene (P-DCX) wherein optionally theparticles may be saturated with Methanol to cause a stabilised crust toform before the material is covered by a fine poro-elastic gauzematerial, or silk.
 28. A speaker system, comprising: a speaker unit; anda cabinet forming a chamber at a back region or side region of thespeaker unit largely filled with a felt comprising of a gas permeableupper layer, ultra-fine particles of gas adsorbing material dispersed athigh concentrations within a fibrous matrix without using binder, and apermeable or impermeable back layer; wherein the gas-adsorbing materialmay be a Metal Organic Framework material treated with a hydrophobiccoating, or an amorphous microporous organic polymer (MOP), featuringcomponent materials with innate hydrophobicity, such asPoly-dichloroxylene (P-DCX).
 29. A microphone system, comprising: atleast one transducer element for converting sound to an electricalsignal; optionally a preamplifier that receives an output from thetransducer element; a housing or cabinet at a back region or side regionof the transducer element; and an active region that comprises at leastone support element and adsorbent material comprising a particulateadsorbent material comprising i) microporous organic polymer (MOP)material, and/or ii) metal organic framework (MOF) material treated witha hydrophobic coating or a membrane.
 30. A mobile electronic devicecomprising the microphone system according to claim
 29. 31. The mobileelectronic device as claimed in claim 30 wherein the mobile electronicdevice is a mobile phone or hearing aid.